Hi MYSELF! Siege is one of the Clan Stronghold's statuses. It makes the Stronghold a target for attacks by enemy and neutral troops. To activate this status, you need to build the Tower of Odin in the Stronghold and spend a certain amount of Precious Dust: https://vikingsweb-support.plarium.com/web/en/guide/clan-stronghold/tower-of-odin

Have fun😇

Thanks